Summary.

The antigenicity of whole rabbit semen or of bull semen in egg yolk citrate and the distribution of antibodies in the serum and in the reproductive tract were studied following either two intramuscular injections with adjuvant or several intravaginal depositions (artificial inseminations) into female rabbits.

Repeated artificial insemination of non-pregnant does with bull semen in egg yolk citrate induced only serum antibodies against egg yolk in two out of five rabbits. Repeated insemination of pregnant does led to serum antibodies against egg yolk, bull seminal plasma, and bull spermatozoa in three out of four rabbits, and to vaginal antibodies against egg yolk and bull seminal plasma in two of these rabbits. The cause of the increased response during pregnancy is not known. After the intramuscular injections of bull semen in egg yolk citrate and adjuvant, antibodies against egg yolk, bull seminal plasma, and bull spermatozoa were found in the serum and throughout the tract.

Repeated insemination of pregnant and non-pregnant rabbits with rabbit semen failed to induce any antibodies. Intramuscular injections with adjuvant into five rabbits led to the presence of sperm agglutinins in the sera of all five rabbits, and to sperm-immobilizing antibodies, a precipitin against seminal plasma, and complement-fixing antibodies against seminal plasma from a vasectomized buck in two of the rabbits. No antibodies could be detected in the tract. Experiments with homologous semen were complicated by the presence of natural complement-fixing activity in rabbit serum against rabbit spermatozoa, and by a heat-stable factor in the uterus causing agglutination of rabbit spermatozoa.

The results are discussed in relation to (a) the non-antigenicity of homologous spermatozoa in rabbits, as compared with the antigenicity of homologous spermatozoa in other species, and (b) the passage of heterologous antigens or of antibodies against these antigens between the serum and the genital tract. It is concluded that intramuscular injection of antigen induces systemic antibodies which then enter the tract, whereas artificial insemination leads to the formation of local tract antibodies and to the passage of antigen into the systemic circulation.

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